the coking properties of coal at elevated pressures. - Argonne ...

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Table I: Compositions of High Temperature Ash (HTA)
Coal Name
Coal Rank
%H TA
Si02(%a)***
A120 (%a)
Ti 023%a)
Fe 20 3( %a )
MgO (%a)
CaO( %a)
Na20( %a)
K20(%a)
P205(%a)
s03( %a)
Trace Elements
>1000ppm of HTA
(in ppm of HTA)
Hagel Seam*
Lignite
9.66
28,20
9.35
0.58
8.20
5,91
24 50
2.81
0.33
0.10
17.40
Ba-6700
Sr-3150
Cumber1 and Fuel **
High Volatile
Bituminous
18.8
51 .3
19.8
002
17.0
1.2
4.9
oo9
2.8
0.2
1.6
Not
Available
Pennsylvania
#2 Seam*
Semianthracite
30.74
80 .OO
12,lO
3.09
1.47
0.05
0.30
0.05
0-35
0,05
0,30
None
Reported
"Information courtesy of the Penn State Coal Data Base
**Information taken from reference (8).
***%a - oxide % of HTA of dry coal
Experimental Procedure
The STEM used in the present study was a JOEL 200CX equipped with a Tracor-
Northern T!42000 energy dispersive spectrometry (EDS) system for x-ray analysis
The features of STEM operation pertinent to this work are illustrated in Figure 1,
The sample was illuminated by a narrow probe of 200kV electrons which was scanned
across its surface. Transmitted electrons were used to form an image of the sample
volume being scanned, The probe could also be stopped and fixed on some feature
of interest in the sample, at which point the characteristic x-rays emitted by the
atoms under the probe could be analyzed to obtain chemical information from a
sample region with a diameter approaching that of the probe diameter. Chemical
characterization could be accomplished in this manner for all elements with atomic
number 2211
For studies of mineral matter embedded in particles of powdered coal, advan-
tage was taken of the difference in image contrast between the crystalline
mineral particles and the surrounding amorphous organic matrix. The crystalline
particles are capable of diffracting electrons, and so appeared in strong contrast
when held at specific angles to the incident electron beam.
needed only to be tilted through some moderate range of angles (generally + 45"
from the horizontal) to quickly establish the locations of the minerals wiThin
a given coal particle. During the tilting such particles abruptly "winked" in and
out of strong diffractiDn contrast, while the amorphous matrix changed contrast
only gradually as a function of the change in sample thickness intercepted by
the electron beam. An example of an image of a mineral particle visible by strong
diffraction contrast amidst an amorphous coal matrix is shown in Figure 2,
estimated that the imaging procedure could detect mineral particles with diameters
>-2nm. Particles smaller than this would most likely remain indistinguishable
from the amorphous matrix,
llith the location of an embedded mineral particle thus determined, the probe
was fixed on the mineral and an x-ray spectrum was acquired, Except in the instance
where the mineral extended through the full thickness of the coal particle
intercepted by the probe, this spectrum consisted of a superposition of a particle
spectrum and a matrix spectrum.
The sample thus
To determine the signal associated with the
It is
inclusion, the probe was subsequently moved 1-2 particle diameters away to a region
of the matrix known to be free of other minerals (within the resolution limitation
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